Is there any Free Software VCS that specifically targets monorepos? If not, which of the "usual" VCS are best suited for monorepos? CVS? Subversion? Darcs? Baz

Is there any Free Software VCS that specifically targets monorepos? If not, which of the "usual" VCS are best suited for monorepos? CVS? Subversion? Darcs? Bazaar? Mercurial? Git? Should one use Mercurial simply because Facebook uses (and patches) it, or are the better choices for small-to-midsize organizations?